1. Field of the Invention
The present invention relates to a delivery cart which includes a chassis formed of longitudinal and cross beams, at least one castor pivotable about a vertical axis and two support wheels for supporting the chassis on a ground, a displacement stirrup attached to the chassis and towering above the chassis, gearless, load-actuated reversible electric motor means associated with at least one castor or two support wheels and formed integrally with the castor or two support wheels, a power source for the electric motor means, and control means for controlling power supply to the electric motor means and including sensor means for sensing a displacement force and/or a steering force applied to the cart, and a control unit for controlling power supply to the electric motor means in accordance with the displacement force and/or a steering force.
2. Description of the Prior-Art.
German Publication DE-OS 195 05 309 describes a motor-driven delivery cart for delivering or distribution of large quantity of goods to a plurality of receiving stations, which permits to deliver a large quantity of different materials with a minimum of manual efforts on the part of a deliverer. Such a delivery cart spares the delivery person from expenditure of substantial physical efforts for moving the cart. In this cart, the power supply to the drive motor is controlled in accordance with a push or pulling force applied to the stirrup by the cart user. Such control not only insures matching of the driving power with the speed intended by the cart operator, independent from the area of the load, i.e., instantaneous total weight of the cart, and independent from whether the cart track rises or falls but also results in a reduced energy consumption. In the known delivery cart, the stirrup is formed as a motor vehicle steering wheel which is connected with the chassis by a single beam or bar, and the cart is provided with sensors for sensing the direction and the magnitude of the beam deformation for controlling the power supply to the electric motors. The use of sensors for sensing the pressure, displacement and deformation forces and for generating appropriate control signals for controlling the power supply to the electric motors is connected with substantial expenditures and considerably limits the possibilities of a correct determination of the drive actuation threshold.
Further, the auxiliary drive and its control, which are used in known delivery carts with an auxiliary power assist, are characterized by an unchangeable construction designed for a specific delivery cart and, therefore, can be used only with newly produced carts. In view of the durability of the carts and in the interest of the economical use of the auxiliary power assist means for a delivery cart, it is desirable to standardize the necessary components so that they can also be used with the already produced carts.
Accordingly, an object of the present invention is an auxiliary drive for a motor-driven delivery cart of the above described type which can be produced with as small as possible technical expenditures and with small as possible costs.
Another object of the present invention is to provide control means which can be used with difference types of the delivery carts, including already operational carts.
A further object of the present invention is to provide a delivery cart with power assist means and which would insure its ergonomically favorable handling and which is optimally maneuverable and operationally reliable.